Method for transmitting control signal using efficient multiplexing

ABSTRACT

A method of transmitting a control signal using efficient multiplexing is disclosed. The present invention includes the steps of multiplexing a plurality of 1-bit control signals within a prescribed time-frequency domain by code division multiple access (CDMA) and transmitting the multiplexed control signals, wherein a plurality of the 1-bit control signals include a plurality of the 1-bit control signals for a specific transmitting side. Accordingly, reliability on 1-bit control signal transmission can be enhanced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/444,100, filed Apr. 2, 2009, which is the National Stage ofInternational Application No. PCT/KR2007/004825, filed Oct. 2, 2007,which claims the benefit of earlier filing date and right of priority toKorean Patent Application Nos. 10-2007-0011533, filed Feb. 5, 2007 and10-2007-0099055, filed Oct. 2, 2007, and U.S. Provisional ApplicationSer. Nos. 60/827,852, filed Oct. 2, 2006 and 60/955,019, filed Aug. 9,2007, the contents of which are hereby incorporated by reference hereinin their entirety.

TECHNICAL FIELD

The present invention relates to a method for transmitting a controlsignal in a multi-carrier mobile communication system, and moreparticularly, to a control signal transmitting method. Although thepresent invention is suitable for a wide scope of applications, it isparticularly suitable for transmitting a control signal reliably inuplink/downlink transmission by multiplexing a plurality of 1-bitcontrol signals efficiently.

BACKGROUND ART

Generally, in a multi-carrier mobile communication system, a basestation performs downlink data packet transmission to user equipments(hereinafter abbreviated UEs) belonging to a cell or each of a pluralityof cells. Meanwhile, a plurality of UEs may exist within a cell. Sinceeach of the UEs is unable to know how a data packet will be transmittedto itself using a prescribed format, when a base station transmits adownlink data packet to a specific UE, the base station should transmitsuch necessary information as an ID of a UE that will receive thecorresponding data packet, a time-frequency domain for carrying the datapacket, a data transmission format including a coding rate, a modulationscheme and the like, HARQ relevant information, and the like in downlinkfor each downlink data packet transmission.

On the contrary, in order to enable a UE to transmit a data packet inuplink, a base station should transmit such necessary information as anID of a UE that will be approved for data packet transmission, an uplinktime-frequency domain enabling the UE to transmit the data packet, adata transmission format including a coding rate, a modulation schemeand the like, HARQ relevant information, and the like in downlink foreach uplink data packet transmission.

In case of the uplink data packet transmission, a base station shouldtransmit reception success acknowledgement/non-acknowledgement(ACK/NACK) information on each data having been transmitted by a UE tothe corresponding UE in uplink. On the other hand, in case of downlinkdata packet transmission, each UE transmits information about receptionsuccess or failure for each data packet having been transmitted by abase station through ACK/NACK information in uplink.

In order to maintain an uplink transmission/reception power of each UEat a proper level, a base station should transmit power controlinformation to each UE in downlink.

Among the above-explained control signals, an ACK/NACK signal, a powercontrol signal or the like is mainly able to indicate the correspondinginformation using one bit and can be named ‘1-bit control signal’.

In order to operate and manage a system efficiently, it is necessary tomultiplex an uplink/downlink control signal for carrying theabove-explained control information, and more particularly, the 1-bitcontrol signal with a data packet and other signals in a time-frequencyresource efficiently.

As a multiplexing scheme normally used for a multi-carrier mobilecommunication system, time division multiple access (TDMA) formultiplexing a plurality of signals by dividing them on a time domain,frequency division multiple access (FDMA) for multiplexing a pluralityof signals by dividing them on a frequency domain, code divisionmultiple access (CDMA) for multiplexing signals on a prescribedtime-frequency domain using an orthogonal code or a pseudo-orthogonalcode, or the like can be used.

Yet, in case that the 1-bit control signal is multiplexed using TDMAand/or FDMA only, since a transmission power of each control signalconsiderably differs, an effect on a neighbor cell may differ on a timedomain and/or a frequency domain.

In particular, when a random cell multiplexes to transmit ACK/NACKsignals for different UEs within a single TTI by TDMA or FDMA forexample, in case that an ACK/NACK signal transmission power for each ofthe UEs considerably differs, a quantity of interference imposed onneighbor cells by the corresponding cell may differ considerably on atime domain or a frequency domain. And, this may have a bad influence onperforming downlink data packet scheduling in a cellular environment ortime-frequency-energy distributions efficiently.

Moreover, in case that a control signal such as an ACK/NACK signal of atransmitting side is lost in the course of downlink/uplink channeltransmission, there may be a problem of reliability on the correspondingsignal transmission.

DISCLOSURE OF THE INVENTION Technical Problem

Technical Solution

Accordingly, the present invention is directed to a method fortransmitting a control signal in a multi-carrier mobile communicationsystem that substantially obviates one or more of the problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a method oftransmitting a plurality of control signals efficiently, by which acontrol signal of a specific transmitting side can be reliablytransmitted in a manner of performing multiplexing efficiently tominimize inter-cell interference in control signal transmission.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method oftransmitting a control signal according to the present inventionincludes multiplexing a plurality of 1-bit control signals within aprescribed time-frequency domain by code division multiple access(CDMA), repeating the multiplexed control signals in different frequencydomains, and transmitting the repeated control signals.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a method oftransmitting a control signal according to the present inventionincludes multiplexing a plurality of 1-bit control signals within aprescribed time-frequency domain by code division multiple access(CDMA), and transmitting the multiplexed control signals, wherein aplurality of the 1-bit control signals include a plurality of the 1-bitcontrol signals for a specific transmitting side.

Preferably, wherein the prescribed time-frequency domain comprises atime-frequency domain within 1 OFDM symbol zone.

Preferably, wherein in case that a time domain used for the controlsignal transmission comprises a single OFDM symbol zone, the repeatingis carried out in a manner of repeating the multiplexed control signalsinto the different frequency domains within the single OFDM symbol zone.

Preferably, wherein in case that a time domain used for the controlsignal transmission comprises a plurality of OFDM symbol zones, therepeating is carried out in a manner of repeating the multiplexedcontrol signals into the different frequency domains within the OFDMsymbol zones differing from each other.

Preferably, in the multiplexing, a plurality of the 1-bit controlsignals are discriminated by an orthogonal or pseudo-orthogonal codeused for multiplexing of each of the 1-bit control signals.

More preferably, a plurality of the 1-bit control signals are modulatedby being discriminated by different orthogonal phase components,respectively and wherein in the multiplexing, a plurality of the 1-bitcontrol signals are additionally discriminated by the differentorthogonal phase components used for the modulation.

Preferably, the prescribed time-frequency domain includes a plurality oftime-frequency domains. In the multiplexing, additional multiplexing iscarried out by at least one selected from the group consisting of timedivision multiple access (TDMA) and frequency division multiple access(FDMA). And, a plurality of the 1-bit control signals for the specifictransmitting side are multiplexed by being spread in a plurality of thetime-frequency domains.

More preferably, the 1-bit control signals for different transmittingsides are multiplexed in a plurality of the time-frequency domains bythe code division multiple access, respectively. In this case, aplurality of the 1-bit control signals for the specific transmittingside are multiplexed by different orthogonal or pseudo-orthogonal codes.

And, the orthogonal or pseudo-orthogonal code includes a code sequencehaving a length corresponding to a size of a plurality of thetime-frequency domains.

Besides, the 1-bit control signal can include either an ACK/NACK signalor a power control signal. And, the 1-bit control signal can betransmitted in either uplink or downlink.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

ADVANTAGEOUS EFFECTS

According to one embodiment of the present invention, in multiplexing aplurality of 1-bit control signals, CDMA is mainly used. And, it is ableto transmit a plurality of controls signals of a specific UE throughdifferent orthogonal or pseudo-orthogonal codes, respectively. Hence, itis able to enhance reliability on the corresponding control signaltransmission.

And, the number of multiplexed signals in coherence bandwidth and/orcoherence time can be increased by carrying out FDMA and/or TDMA on the1-bit control signal transmission side by side and by distributing totransmit a plurality of control signals for a specific UE on eachtime-frequency domain.

Moreover, in case of transmitting the 1-bit control signal through aplurality of time-frequency domains, by specifying to use an orthogonalcode used for transmission in accordance with the size the wholetime-frequency domains instead of the size of each the time-frequencydomain, it is able to increment a number of control signals that can besimultaneously transmitted.

Besides, in case that a plurality of OFDM symbols are used for 1-bitcontrol signal transmission, by transmitting a CDMA modulated 1-bitcontrol signal on a different OFDM symbol area through a differentfrequency domain, it is able to perform efficient transmission inaspects of resource efficiency and diversity gain. And, it is also ableto make a power allocation more flexible within each OFDM symbol area.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a diagram for explaining a method of multiplexing to transmitACK/NACK signals by CDMA according to one embodiment of the presentinvention;

FIG. 2 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA and FDMAaccording to one embodiment of the present invention;

FIG. 3 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA, TDMA andFDMA according to one embodiment of the present invention;

FIG. 4 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA and FDMAaccording to one embodiment of the present invention, in which aplurality of ACK/NACK signals transmitted by a specific transmittingside among a plurality of ACK/NACK signals are transmitted through aplurality of frequency domains;

FIG. 5 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA, TDMA andFDMA according to one embodiment of the present invention, in which aplurality of ACK/NACK signals transmitted by a specific transmittingside among a plurality of ACK/NACK signals are transmitted through aplurality of time-frequency domains;

FIG. 6 is a diagram for explaining a method of transmitting ACK/NACK incase of using 1 OFDM symbol zone for ACK/NACK transmission according toone embodiment of the present invention;

FIG. 7 is a diagram for explaining a method of transmitting ACK/NACK incase of using at least 2 OFDM symbol zones for ACK/NACK transmissionaccording to one embodiment of the present invention;

FIG. 8 is a diagram for explaining a method of transmitting ACK/NACK incase of using at least 2 OFDM symbol zones for ACK/NACK transmissionaccording to one preferred embodiment of the present invention; and

FIG. 9 is a diagram to explain a principle that power allocationflexibility is increased in case of transmitting ACK/NACK signals by theembodiment shown in FIG. 8.

BEST MODE Mode for Invention

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Generally, a base station transmits an ACK/NACK signal indicating asuccess or failure in receiving a data packet transmitted by each UEwithin a cell or a control signal playing a role similar to that of theACK/NACK signal to the corresponding UE in downlink. In doing so, sincea plurality of UEs are able to transmit uplink data packets within asingle TTI, the base station is able to transmit ACK/NACK signals to aplurality of the UEs within a single TTI as well.

And, a base station multiplexes a plurality of power control signals forcontrolling transmission powers of uplink data of a plurality of UEs fora single TTI within a cell and then transmits the multiplexed signal toeach of the UEs.

Hence, according to one embodiment of the present invention, in order tomultiplex and transmit a plurality of 1-bit control signals efficiently,a method of multiplexing to transmit a plurality of 1-bit controlsignals by CDMA within a partial time-frequency domain of a transmissionband in a multi-carrier system is proposed. And, this will be explainedwith reference to a detailed example.

Meanwhile, the description for one embodiment of the present inventionrelates to a case that a 1-bit control signal is an ACK/NACK signal forexample. In a control signal transmitting method according to oneembodiment of the present invention, a 1-bit control signal needs not tobe an ACK/NACK signal necessarily. And, it is apparent to those skilledin the art that the present invention includes a random 1-bit controlsignal in a format that a plurality of signals are transmitted within 1TTI.

FIG. 1 is a diagram for explaining a method of multiplexing to transmitACK/NACK signals by CDMA according to one embodiment of the presentinvention.

Referring to FIG. 1, according to one embodiment of the presentinvention, a base station reserves a specific time-frequency domainwithin 1 TTI for ACK/NACK transmission to use. And, ACK/NACK signals fordifferent UEs are discriminated from each other by an orthogonal orpseudo-orthogonal code multiplied on a time-frequency domain.

In this case, the ‘orthogonal code’ or the ‘pseudo-orthogonal code’ is acode used for signal multiplexing in CDMA and means a code thatindicates that a correlation is 0 or a value smaller than a prescribedthreshold.

According to one preferred embodiment of the present invention, in caseof performing a transmission through modulation that uses componentshaving phases orthogonal to each other like QPSK, a plurality ofACK/NACK signals can be additionally discriminated through the differentorthogonal phase components.

In an example shown in FIG. 1, since an ACK/NACK signal is transmittedthrough a time-frequency domain including 12 subcarriers across six OFDMsymbols within a single TTI, it is able to use an orthogonal code havinga chip length 72 (=6×12) for the ACK/NACK transmission. Hence, it ispossible to simultaneously transmit 72 different orthogonal signals.Yet, a number of simultaneously transmittable orthogonal signals mayvary in accordance with a type of a used orthogonal/pseudo-orthogonalcode.

In case of using QPSK as a modulation scheme in the example shown inFIG. 1, it is able to use two orthogonal phases. Hence, it is able totransmit different orthogonal signals amounting to a double of theseventy-two orthogonal signals.

Meanwhile, an ACK/NACK signal for a single UE can be transmitted via asingle orthogonal signal among the orthogonal signals generated by theabove-explained method. Yet, one embodiment of the present inventionproposes that an ACK/NACK signal for a single UE is set to betransmitted via a plurality of orthogonal signals if the single ACK/NACKsignal carries information exceeding 1 bit or if a single UE transmits aplurality of data packets for a single TTI.

Like the above-explained one embodiment of the present invention, anadvantage in multiplexing to transmit an ACK/NACK signal by CDMA indownlink lies in that a quantity of interference generated in downlinkby an ACK/NACK signal on a time-frequency domain of a single TTI can bemaintained relatively equal.

In particular, if a random cell multiplexes to transmit ACK/NACK signalsfor different UEs by TDMA or FDMA within a single TTI, as mentioned inthe foregoing description, if ACK/NACK signal transmission powers forthe respective UEs considerably differ from each other, an interferencequantity having influence on neighbor cells by the corresponding cellcan vary on a time domain or a frequency domain considerably. And, thismay have bad influence on performing downlink data packet scheduling orother time-frequency-energy distribution in a cellular environment. Yet,in case that an ACK/NACK signal is multiplexed by CDMA like oneembodiment of the present invention, even if different ACK/NACK signaltransmission powers are allocated to different UEs, ACK/NACK signals forthe entire UEs are added together within a same time-frequency domainfor a single TTI and then transmitted. Hence, fluctuation oftransmission power on a time-frequency domain can be minimized.

Like one embodiment of the present invention, in case that a pluralityof ACK/NACK signals transmitted by a single UE or for data transmissionof a single UE are transmitted via a plurality of orthogonal signals, itis able to enhance reliability of ACK/NACK signal transmission to thecorresponding UE.

Moreover, the above-explained principle for the downlink transmission ofthe ACK/NACK signal is identically applicable to uplink transmission.

Meanwhile, in multiplexing ACK/NACK signal by CDMA, as mentioned in theforegoing description, orthogonality between the different ACK/NACKsignals multiplexed by CDMA can be maintained only if a downlink radiochannel response characteristic is not considerably changed on atime-frequency domain for carrying the ACK/NACK signal. Hence, it isable to obtain satisfactory reception performance without applying aspecial reception algorithm such as a channel equalizer in a receivingend. Preferably, CDMA multiplexing of ACK/NACK signal is carried outwithin a time-frequency domain, in which a radio channel response is notconsiderably changed, i.e., within a coherent time and a coherentbandwidth.

According to a detailed embodiment of the present invention, a CDMAmultiplexing scheme of ACK/NACK signal can be carried out side by sidewith a FDMA or TDMA multiplexing scheme to narrow a time-frequencydomain for multiplexing ACK/NACK signal by COMA within a coherent rangein which a radio channel response characteristic is not considerablychanged. This is explained as follows.

FIG. 2 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA and FDMAaccording to one embodiment of the present invention.

Referring to FIG. 2, different ACK/NACK signals can be transmitted intime-frequency domains separated from each other on two frequency axes.And, different ACK/NACK signals can be multiplexed by CDMA in each ofthe time-frequency domains. In this case, according to one embodiment ofthe present invention, as ACK/NACK signals are transmitted through twofrequency domains, it can be observed that a width of each of thefrequency domains is set to a 6-subcarrier zone narrower than a12-subcarrier zone.

In particular, in the example shown in FIG. 2, since each of the twotime-frequency domains includes six OFDM symbols and twelve subcarriers,it is able to transmit 36 (=6×6) orthogonal signals by CDMA. Since twotime-frequency domains are used within a single TTI, it is able totransmit 72 (=36×2) orthogonal signals.

In case that QPSK modulation is used, since ACK/NACK signal can beadditionally discriminated using two orthogonal phases, it is able totransmit different orthogonal signals amounting to two times of the 72orthogonal signals.

FIG. 3 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA, TDMA andFDMA according to one embodiment of the present invention.

In particular, FIG. 3 shows an example that multiplexing is carried outon ACK/NACK signals side by side with CDMA, FDMA and TDMA.

Referring to FIG. 3, different ACK/NACK signals can be transmitted onfour time-frequency domains having less channel variations. And,different ACK/NACK signals can be multiplexed in each of thetime-frequency domains by CDMA.

In particular, in the example shown in FIG. 3, since each of thetime-frequency domains includes three OFDM symbols and six subcarriers,it is able to transmit 18 (=3×6) ACK/NACK signals in each domain byCDMA. Since four time-frequency domains are used within a single TTI, itis also able to transmit 72 (=18×4) ACK/NACK signals. Since twoorthogonal phases are usable for QPSK transmission, it is able totransmit a double of the different ACK/NACK signals.

In the above-explained ACK/NACK signal multiplexing scheme shown in FIG.2 or FIG. 3, the scheme for transmitting the different ACK/NACK signalsin each of the time-frequency domains is more advantageous than that ofFIG. 1 in that each of the ACK/NACK signals can be transmitted withinthe time-frequency domain having not considerable fluctuation of theradio channel response characteristic. Yet, in case that a radio channelquality for a prescribed UE in the time-frequency domain for carryingthe ACK/NACK signals is poor, ACK/NACK reception performance of thecorresponding UE can be considerably degraded.

Hence, one embodiment of the present invention proposes that ACK/NACKsignals for a specific UE within a single TTI are transmitted acrosstime-frequency domains distant from a plurality of time-frequency axes.And, one embodiment of the present invention also proposes a scheme forobtaining a time-frequency diversity gain for ACK/NACK signal receptionin a receiving end by multiplexing ACK/NACK signals for different UEs byCDMA in each time-frequency domain.

FIG. 4 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA and FDMAaccording to one embodiment of the present invention, in which aplurality of ACK/NACK signals transmitted by a specific transmittingside among a plurality of ACK/NACK signals are transmitted through aplurality of frequency domains.

Referring to FIG. 4, a receiving side is able to obtain a frequencydiversity gain in a manner that an ACK/NACK signal is transmitted acrosstwo different frequency domains. In the example shown in FIG. 4, anACK/NACK signal is transmitted across two time-frequency domains anddifferent ACK/NACK signals are multiplexed in each of the time-frequencydomains.

In particular, since each of the time-frequency domains includes sixOFDM symbols and six subcarriers, there exist 36 (6×6) ACK/NACK signalsthat can be multiplexed by CDMA in each of the time-frequency domains.Since two orthogonal phases are usable for QPSK transmission, it is ableto transmit a double of the different ACK/NACK signals.

As mentioned in the foregoing description, in multiplexing differentACK/NACK signals within each of the time-frequency domains using anorthogonal code regulated in accordance with the size of eachtime-frequency domain, ACK/NACK signals transmitted via differenttime-frequency domains for a specific UE can be multiplexed using thesame orthogonal code among orthogonal codes used for each of thetime-frequency domains.

Yet, one embodiment of the present invention proposes that ACK/NACKsignals transmitted via different time-frequency domains for a specificUE are multiplexed using different orthogonal codes among orthogonalcodes used for each of the time-frequency domains.

Thus, in case that ACK/NACK signals for a specific UE are multiplexedusing different orthogonal codes in each domain, it is able to preventreception performance from being reduced by special orthogonalityreduction influence with other ACK/NACK signals with which a specificACK/NACK signal is CDMA multiplexed for a specific TTI. And, this schemecan be extended to enable ACK/NACK signal of a specific UE to betransmitted using different orthogonal codes in different time-frequencydomains even if the ACK/NACK signal is transmitted via at least threetime-frequency domains.

In case that ACK/NACK signals are transmitted via a plurality oftime-frequency domains, as shown in FIG. 4, one preferred embodiment ofthe present invention proposes that more ACK/NACK signals can besimultaneously transmitted in a manner of specifying orthogonal codes inaccordance with the size of the entire domains instead of specifying anorthogonal code in accordance with in the size of each thetime-frequency domain and then transmitting a plurality of ACK/NACKsignals correspondingly.

In particular, in the example shown in FIG. 4, by obtaining 72orthogonal codes in accordance with 72 (=6×12) chip length according tosix OFDM symbols and 12 subcarriers belonging to two time-frequencydomains for carrying a plurality of ACK/NACK signals of a specific UEinstead of 36 chip length according to six OFDM symbols and sixsubcarriers belonging to a single time-frequency domain, it is able tosimultaneously transmit 144 ACK/NACK signals using different orthogonalphases in case of using QPSK transmission.

In this case, a problem generated from a fact that orthogonality betweenorthogonal codes is reduced due to a considerable difference betweenradio channel responses of different time-frequency domains can beovercome by allocating ACK/NACK transmission powers differing from eachother in accordance with partial cross correlation characteristicsbetween orthogonal codes.

In particular, if transmission powers of orthogonal codes within acorresponding group are matched by grouping codes decided as having loworthogonality among the above-specified orthogonal codes, the aboveorthogonality problem can be solved.

FIG. 5 is a diagram for explaining a method of transmitting ACK/NACKsignals by carrying out multiplexing side by side with CDMA, TDMA andFDMA according to one embodiment of the present invention, in which aplurality of ACK/NACK signals transmitted by a specific transmittingside among a plurality of ACK/NACK signals are transmitted through aplurality of time-frequency domains.

FIG. 5 shows an example that a time-frequency diversity gain is obtainedin a manner that ACK/NACK signals for a specific UE are transmittedacross two different time-frequency domains.

In particular, ACK/NACK signals for UEs 1 to N/4 are transmitted via atime-frequency domain placed in a left upper part of FIG. 5 and atime-frequency domain placed in a right lower part of FIG. 5, whileACK/NACK signals for UEs N/4+1 to N/2 are transmitted via atime-frequency domain placed in a left lower part of FIG. 5 and atime-frequency domain placed in a right upper part of FIG. 5.

In particular, ACK/NACK signals for a specific UE in the example shownin FIG. 5 are transmitted across two time-frequency domains. DifferentACK/NACK signals are multiplexed by CDMA within each of thetime-frequency domains and then transmitted.

Moreover, eighteen ACK/NACK signals can be transmitted via orthogonalcodes corresponding to 18 (=3×6) chip length across three OFDM symbolsand six subcarriers within each of the time-frequency domains. Since twoorthogonal phases are usable for QPSK transmission, it is able totransmit 36 different ACK/NACK signals amounting to a double of theformer ACK/NACK signals.

In the example shown in FIG. 5, it is able to discriminate ACK/NACKsignals transmitted via different time-frequency domains for a specificUE from other ACK/NACK signals using the same orthogonal code. Yet, adiversity gain can be obtained by multiplexing the ACK/NACK signalswithin each of the time-frequency domains using different orthogonalcodes.

Moreover, in the example shown in FIG. 5, in case that orthogonal codesare specified with reference to in the size of the entire time-frequencydomains instead of specifying orthogonal codes with reference to in thesize of each time-frequency domain, it is able to transmit more ACK/NACKsignals simultaneously.

In particular, by specifying orthogonal codes not for chip lengthconstructed with three symbols and six subcarriers included in each ofthe time-frequency domains but for 72 chip length constructed with totalsix OFDM symbols and 12 subcarriers, it is able to transmit moreACK/NACK signals simultaneously.

In the above-explained embodiments shown in FIGS. 1 to 5, a 1-bitcontrol signal such as an ACK/NACK signal is transmitted by spreading in3 or 6 OFDM symbol zones by CDMA for example. Yet, an OFDM symbol zoneusable for transmission of 1-bit control signal such as ACK/NACK signalcan include at least one or more OFDM symbols.

Among the 1-bit control signal (ACK/NACK signal) transmitting methodsaccording to the above-explained embodiments of the present invention,the method of transmitting ACK/NACK signals repeatedly in a plurality oftime-frequency domains to secure the transmission diversity gain can bediversified in accordance with a number of available OFDM symbol zones.In the following description, a method of transmitting ACK/NACKefficiently in accordance with a number of OFDM symbols used for theACK/NACK signal transmission is described.

FIG. 6 is a diagram for explaining a method of transmitting ACK/NACK incase of using 1 OFDM symbol zone for ACK/NACK transmission according toone embodiment of the present invention.

In detail, FIG. 6 shows that four ACK/NACK signals are spread at aspreading factor (SF) 4 in 1 OFDM symbol zone, multiplexed by CDMA andthen transmitted. In FIG. 6, a single box indicates a single subcarrierzone. And, A_(ij) indicates an ACK/NACK signal multiplexed by CDMA. Inthis case, ‘i’ is an index of a spread and multiplexed signal and ‘j’ isan index indicating a group of the multiplexed ACK/NACK signal. AnACK/NACK group indicates a set of the multiplexed ACK/NACK signals. And,a plurality of ACK/NACK groups can exist in accordance with necessity ofeach system and a resource situation. For clarity and convenience, FIG.6 assumes that there exists a single ACK/NACK group only.

Since the present embodiment assumes a case that a single OFDM symbol isused for ACK/NACK transmission only, it is unable to obtain a diversitygain on a time axis for ACK/NACK signal transmission.

Yet, to obtain a diversity gain on a frequency axis, ACK/NACK signalsmultiplexed on the frequency axis by CDMA can be repeatedly transmittedin different frequency domains.

FIG. 6 shows an example that ACK/NACK signals multiplexed by CDMA arefour times repeated in different frequency domains. In this case, thefour times repetition is just an example to obtain diversity. A count ofrepetitions can vary in accordance with a channel status and a resourcesituation of system. In FIG. 6, each of the four times repeated ACK/NACKsignals has the same indices (i, j) for emphasizing the repetition ofthe signals. But, each of the four times repeated ACK/NACK signals canbe multiplexed by different orthogonal code or like, so in this case,these signals can be a different signal to each other. But, forconvenience of explanation, this possibility of differentiation of eachrepeated signal will be ignored in the whole context.

FIG. 6 deals with a case that a single OFDM symbols is used for ACK/NACKtransmission. The case of using a single OFDM symbols is just an examplefor describing the present invention. And, the present invention isapplicable to a case of using a plurality of OFDM symbols as well.

In more particularly, in case that ACK/NACK is transmitted via severalOFDM symbols, repetition on a time axis is also applicable as well as arepetition on a frequency axis in order to obtain additional diversityas well as transmitting antenna diversity.

In the following description, a case of using a plurality of OFDMsymbols for ACK/NACK signal transmission is described.

In case that OFDM symbols for ACK/NACK transmission are incremented, itis able to use ACK/NACK signals in case of using a single OFDM symbolfor ACK/NACK transmission can be repeatedly used for the incrementedOFDM symbols intactly. In this case, since the OFDM symbols used for theACK/NACK transmission are incremented, it is able to more power of asignal used for the ACK/NACK transmission. Hence, it is able to transmitthe ACK/NACK signals to a wider area of a cell.

FIG. 7 is a diagram for explaining a method of transmitting ACK/NACK incase of using at least 2 OFDM symbol zones for ACK/NACK transmissionaccording to one embodiment of the present invention.

FIG. 7 shows an ACK/NACK signal transmitting method when a number ofOFDM symbols for ACK/NACK signal transmission is incremented into 2, intransmitting ACK/NACK signals having the same spreading factor as FIG.6. In particular, FIG. 7 shows a case that a structure in using a singleOFDM symbol for ACK/NACK transmission like FIG. 6 is intactly andrepeatedly applied to a second OFDM symbol.

In case of the transmission with the above structure, even if a symbolnumber is incremented, the number of transmittable ACK/NACK signals isequal to that of the case of using a single OFDM symbol. This is becausemore time-frequency resources are used for the transmission of the samenumber of ACK/NACK signals by substantially incrementing thetime-frequency repetition count as more OFDM symbols are used for theACK/NACK signals repeated on the frequency axis only in case of using asingle OFDM symbol only.

In case of performing the transmission by this method, more power can beallocated to the ACK/NACK transmission but waste or resource may takeplace. In case that more OFDM symbols are used for the ACK/NACK signaltransmission to reduce the waste of resource, if a transmission isperformed by decrementing the repetition count on the frequency axis perthe OFDM symbol, the same time-frequency domain as the case of using asingle OFDM symbol can be occupied. Hence, it is able to utilizeresources more efficiently.

FIG. 8 is a diagram for explaining a method of transmitting ACK/NACK incase of using at least 2 OFDM symbol zones for ACK/NACK transmissionaccording to one preferred embodiment of the present invention.

FIG. 8 shows an example that resources are more efficiently utilized bydecrementing a frequency axis repetition count of ACK/NACK signalsmultiplexed by CDMA in case that the number of OFDM symbols for ACK/NACKsignal transmission are incremented into two.

Although ACK/NACK signals are repeated twice compared to four times inFIG. 6, as the number of OFDM symbols used for the ACK/NACK signaltransmission is incremented, the use of four time-frequency resourcedomains is the same as the case of using a single OFDM symbol.

Compared to FIG. 7 which shows the case of performing transmission byapplying the same ACK/NACK signal structure to the entire OFDM symbols,assuming that the same time-frequency resource is used, FIG. 8 showsthat ACK/NACK signal transmission is possible twice. Hence, resourcescan be more efficiently used.

Comparing to FIG. 7, since the number of, time-frequency resourcedomains used for the ACK/NACK signal transmission is decremented, asignal power for the ACK/NACK signal transmission may become less. Yet,since the overall ACK/NACK signals are transmitted across thetime-frequency domain, more efficient transmission power allocation persymbol is possible rather than the case of transmitting the ACK/NACKsignals using a single OFDM symbol only.

Referring to FIG. 8, when a plurality of OFDM symbol zones are used forACK/NACK transmission, in case that the method of transmitting aspecific ACK/NACK signal via a different frequency domain in each OFDMsymbol zone according to the present embodiment is taken, it is moreadvantageous that power allocation to each ACK/NACK signal can becarried out more flexibly rather than the method of transmittingACK/NACK via different frequency domains within each OFDM symbol zone.This is explained in detail with reference to FIG. 9 as follows.

FIG. 9 is a diagram to explain a principle that power allocationflexibility is increased in case of transmitting ACK/NACK signals by theembodiment shown in FIG. 8.

In (a) and (b) of FIG. 9, A₁, A₂, A₃ and A₄ indicate ACK/NACK signalgroups multiplexed by CDMA, respectively. In particular, (a) of FIG. 9shows a format that CDMA-multiplexed ACK/NACK signals are transmitted bybeing repeated in different frequency domains within a same symbol zone.And, (b) of FIG. 9 shows a format that CDMA-multiplexed ACK/NACK signalsof the present embodiment are transmitted by being repeated in differentfrequency domains within different OFDM symbol zones, respectively.

In case that ACK/NACK signals are transmitted in a same manner shown in(a) of FIG. 9, total powers allocated to the respective OFDM symbolzones should be allocated by being distributed to two ACK/NACK signals.On the contrary, in case that ACK/NACK signals are transmitted in a samemanner shown in (b) of FIG. 9, total powers allocated to the respectiveOFDM symbol zones can be allocated by being distributed to four ACK/NACKsignals. Hence, flexibility of power allocation can be enhanced morethan that of the case shown in (a) of FIG. 9.

In other words, when the number of OFDM symbol zones available forACK/NACK transmission is plural like the present embodiment, in casethat ACK/NACK signals are transmitted via different frequency domains indifferent OFDM symbols, flexibility in power allocation is enhanced todiversify power allocation for ACK/NACK signals per a user.

In the above-explained embodiment of the present invention, a spreadingfactor for multiplexing of a plurality of ACK/NACK signals, a repetitioncount in time-frequency domain, and the number of OFDM symbols forACK/NACK signal transmission are just exemplary for the accurateexplanation of the present invention but other spreading factors, otherrepetition counts and various numbers of OFDM symbols are applicable tothe present invention.

In the above-described example for explaining the present invention inaccordance with the time-frequency resource, a case of using a singletransmitting antenna that does not use transmitting antenna diversity isrepresented only. Alternatively, the present invention is alsoapplicable to the case of using a two transmitting antennas diversityscheme or a four transmitting antennas diversity scheme.

It is apparent to those skilled in the art that the above-explainedscheme for obtaining the time-frequency diversity gain from the ACK/NACKsignal transmission can be used side by side with the scheme of usingFDMA or TDMA as well as the case of using CDMA for the multiplexing ofdifferent ACK/NACK signals according to one embodiment of the presentinvention.

The above-explained multiplexing and transmission schemes of ACK/NACKsignals are identically applicable to the multiplexing and transmissionscheme of a plurality of power control signals transmitted to differentUEs in downlink. Particularly, a downlink ACK/NACK signal and a downlinkpower control signal can be transmitted by being multiplexed in the sametime-frequency domain by CDMA.

Moreover, the above-explained ACK/NACK signal multiplexing andtransmission schemes are identically applicable to uplink ACK/NACKsignal transmission for data packets transmitted in downlink as well.

Moreover, if the number of OFDM symbols used for transmission ofACK/NACK signal can be variable in a specific system, it is preferablethat the number of repetition of ACK/NACK signal is decreased inaccordance with the increase of the OFDM symbols used.

INDUSTRIAL APPLICABILITY

According to one embodiment of the present invention, in multiplexing aplurality of 1-bit control signals, a plurality of control signals of aspecific UE can be transmitted via orthogonal or pseudo-orthogonal codesdiffering from each other using CDMA mainly. Hence, the presentinvention enhances reliability on a corresponding control signaltransmission.

And, frequency and/or time diversity can be obtained by carrying outFDMA and/or TDMA on the 1-bit control signal transmission side by sideand by distributing to transmit a plurality of control signals for aspecific UE on each time-frequency domain.

Moreover, in case of transmitting the 1-bit control signal through aplurality of time-frequency domains, by specifying to use an orthogonalcode used for transmission in accordance with the size of the wholetime-frequency domains instead of in the size of each time-frequencydomain, it is able to increment a number of control signals that can besimultaneously transmitted.

Besides, in case that a plurality of OFDM symbols are used for 1-bitcontrol signal transmission, by transmitting a CDMA modulated 1-bitcontrol signal on a different OFDM symbol area through a differentfrequency domain, it is able to perform efficient transmission inaspects of resource efficiency and diversity gain. And, it is also ableto make a power allocation more flexible within each OFDM symbol area.

Accordingly, a control information transmitting method according to thepresent invention has a configuration suitable to be applied to 3GPP LTEsystem. Moreover, a control information transmitting method according tothe present invention is applicable to random communication systems thatrequire specifications for a control information transmission format intime-frequency domain as well as to the 3GPP LTE system.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

1. A method of transmitting ACK/NACK signals, the method comprising:repeating each of the ACK/NACK signals by N times, wherein N is apredetermined natural number greater than 1; multiplexing i-th bits,each of the i-th bits being from the repeated ACK/NACK signalsrespectively, within an i-th time-frequency domain by a Code DivisionMultiple Access (CDMA) scheme, wherein i=1, 2, . . . , N, and the i-thtime-frequency domains, each of which is for i=1, 2, . . . , N,respectively, are different from each other; and transmitting themultiplexed ACK/NACK signals, wherein the ACK/NACK signals arediscriminated by orthogonal or pseudo-orthogonal codes used formultiplexing of each of the ACK/NACK signals.
 2. The method of claim 1,wherein a number of the ACK/NACK signals corresponds to a number of theorthogonal or pseudo-orthogonal codes used for multiplexing of each ofthe ACK/NACK signals.
 3. The method of claim 1, wherein the multiplexedACK/NACK signals are mapped to different frequency regions within asingle OFDM symbol zone, when a time zone used for transmitting themultiplexed ACK/NACK signals is the single OFDM symbol zone.
 4. Themethod of claim 1, wherein the multiplexed ACK/NACK signals are mappedto different frequency regions within a plurality of OFDM symbol zonesdifferent from each of the plurality of OFDM symbol zones, when a timezone used for transmitting the multiplexed ACK/NACK signals is theplurality of OFDM symbol zones.
 5. A method of transmitting signals, themethod comprising: generating N bit control signals by repeating each ofACK/NACK signals; multiplexing i-th bits, each of the i-th bits beingfrom the N bit control signals respectively, within an i-thtime-frequency domain by a Code Division Multiple Access (CDMA) scheme,wherein i=1, 2, . . . , N, and the i-th time-frequency domains, each ofwhich is for i=1, 2, . . . , N, respectively, are different from eachother; and transmitting the multiplexed N bit control signals, whereinthe ACK/NACK signals are discriminated by orthogonal orpseudo-orthogonal codes used for multiplexing each bits from the N bitcontrol signals, and wherein a number of ACK/NACK signals is twice asmany as a size of the orthogonal or pseudo-orthogonal codes.